The curious move by F1's Lewis Hamilton to Mercedes

Formula One is scratching its collective head over why former champion Lewis Hamilton is leaving McLaren after this year to join the Mercedes GP team.

Hamilton, 27, won his 2008 championship with McLaren and, at the moment at least, it would seem McLaren remains a stronger team than Mercedes.

The British driver hasn't won another F1 title since 2008 and has had problems on the track at times this season. Yet he does have three wins this year and is fourth in the point standings.

The Mercedes team, meanwhile, largely has struggled since taking over the Brawn GP team in 2010, although Mercedes' Nico Rosberg won in China this year.

Rosberg's teammate Michael Schumacher, the seven-time champion who came out of retirement to join Mercedes in 2010, seldom has been unable to stay up front and will lose his ride upon Hamilton's arrival.

So why is Hamilton moving? Hamilton said he wanted "to take on a fresh challenge" and, indeed, Hamilton's ties to McLaren include not only his six seasons in F1 but stretch back to his years in developmental racing.

Apparently money wasn't a huge factor in his decision, either. Three-time champion Niki Lauda, who is set to become the Mercedes team's non-executive chairman, told BBC Radio that he met with Hamilton and the offers from both teams were "very close."

It was the challenge of trying to win another world championship, this time with Mercedes, that appealed to Hamilton, whose aproach to the decision was "very pragmatic" and with "no emotions whatsoever," Lauda said.

In the meantime, Hamilton remains with McLaren as the series next holds the Japanese Grand Prix on Sunday.

On Nov. 18, Formula One returns to the United States for the first time in five years with a race in Austin, Texas.